Determining intensity dependence of ultrashort laser processes through focus z-scanning intensity-difference spectra: application to laser-induced dissociation of H+2

A focal spot scanning intensity-difference spectra method is developed to allow one to determine the intensity dependence of laser produced features while improving experimental statistics. This method is applicable to focused Gaussian beam interactions with approximately uniform planar targets. Furthermore, it can be applied to disentangle the intensity dependence of thick targets. The usefulness of this method is demonstrated by applying it to the kinetic energy release spectrum resulting from the dissociation of an H+2 beam in an intense ultrashort laser pulse.